Reducing Radon in New Construction of ANSI/AARST CCAH 2020 1 & 2 Family Dwellings and Townhouses 3 INCHES OF WATER COLUMN (in. WC). A measure of pressure. CONVERSION: 1 in. WC = 249 Pascals . KARST. An area underlain by limestone in which erosion has produced fissures, sinkholes, underground streams, or caverns. LICENSED. A designation applied to individuals and/or companies that are qualified and specifically authorized as radon laboratories, measurement and/or mitigation professionals within certain states or jurisdictions that regulate radon services. Also see CERTIFIED. MIL. 1mil=1/1000 of an inch = 0.0254 millimeters. NATIONAL ACTION LEVEL (NAL). The indoor radon concentration at which mitigation is recommended. The NAL is defined as the US Environmental Protection Agency’s Action Level of 4 pCi/L [148 Bq/m 3 ]. OUTDOOR AMBIENT RADON LEVELS. The amount of radon naturally occurring in outdoor air at a locality. The annual US national average outdoor radon level is 0.4 pCi/L [15 Bq/m 3 ] but local conditions will vary. OUTLET. A point on the wiring system at which current is taken to supply utilization equipment. PASCAL [Pa]. A measure of pressure. CONVERSION: 1 Pa = 0.004 Inches of Water (in. WC). PICOCURIES PER LITER (pCi/L). A unit of measure for the amount of radioactivity in a liter of air. CONVERSION: 1.0 pCi/L = 37 Bq/m 3 . PIPE LOOP. A continuous length of perforated pipe extending around the inside perimeter of the foundation. RADON. A naturally occurring, chemically inert, radioactive element (Rn-222) which exists as a gas. RADON CONTROL SYSTEM. A system designed to reduce radon concentrations in indoor air. ROUGH-IN. The installation of all parts and materials of an ASD system that must be completed prior to the placement of concrete, closure of building cavities and installation of finish materials. Such parts and materials are gas permeable layers, soil gas retarders , plenums, membranes, piping, suction points , discharge point and wiring. SOIL GAS. The gas mixture present in soil that could contain radon , water vapor and other gases. SOIL GAS COLLECTION PLENUM. A constructed enclosure for collecting radon and other soil gases from under a foundation. SOIL GAS COLLECTOR. A gas permeable conduit constructed of gravel , perforated pipe or geotextile matting for collecting radon and other soil gases from within a soil gas collection plenum and connecting the plenum to the ASD pipe system. SOIL GAS RETARDER. A continuous membrane or other comparable material laid over a soil gas collection plenum or earthen floor area that is used to retard the flow of soil gases into a building. SUB-MEMBRANE DEPRESSURIZATION. A radon mitigation technique designed to maintain lower air pressure in the space under a soil gas retarder membrane than above it by use of an ASD fan drawing air from beneath the membrane. SUB-SLAB DEPRESSURIZATION. A radon mitigation technique designed to maintain lower air pressure under a floor slab than above it by use of an ASD fan installed in the radon system piping that draws air from below the floor slab. SUCTION POINT. Location where the soil gas collector is connected to the rough-in or ASD system piping. TOWNHOUSE. A single family dwelling unit constructed in a group of three or more attached units where each unit extends from the foundation to the roof and has a yard or public way on at least two sides.